JPH0530887B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the extraction of gold and possibly other metals from difficult-to-smelt gold-bearing sulphide concentrates. It is known that the extraction of gold from such concentrates by conventional methods such as cyanization is not satisfactory;
Various pretreatment methods have been proposed. However, for various reasons, the pretreatments proposed in the prior art have not improved the extraction of gold from such concentrates as much as would be desirable for commercial operations. It is therefore an object of the present invention to propose an improved pretreatment method for such concentrates, including a pressure oxidation treatment. The present invention provides a method for extracting gold from concentrate containing gold and iron-containing sulfides, which are difficult to smelt, and which includes supplying the concentrate as an aqueous slurry to an acidic pretreatment step, and the acidic pretreatment step. The concentrate is treated with an aqueous sulfuric acid solution to destroy carbonates and acid-consuming gangue compounds that may otherwise interfere with the subsequent pressure oxidation process, and the treated slurry is subjected to the pressure oxidation process. under a pressurized oxidizing atmosphere at a temperature in the range of about 135 to about 250°C, while preferably maintaining a free acid concentration of about 5 to about 40°C during the oxidation step.
g/L sulfuric acid to dissolve the iron, form sulfuric acid, and remove substantially all of the oxidizable sulfide compounds into the sulfate form in which less than about 20% of the oxidized sulfur is present as elemental sulfur. and adding water to the oxidized slurry in a first repulping step so that the pulp density ranges from about 5% to about 15% solids by weight. producing a re-mineralizing oxidized slurry; subjecting the re-mineralizing oxidized slurry to a liquid-solid separation step to produce a solution containing acid and iron and an oxidized and separated solid content; recycling a portion of the acid and iron containing solution to the acidic pretreatment step and removing gold from the oxidized and separated solids. The method may include recycling a portion of the solution containing acid and iron to the oxidation step. In addition, in this method, a precipitant is added to a part of the solution containing the acid and iron in the precipitation step, and the metals are converted into their respective hydroxides or hydrated oxides.
The method may include precipitating the sulfate ion as an insoluble sulfate and the arsenic as an insoluble arsenate, separating the precipitate from the remaining aqueous solution, and utilizing at least some of the separated aqueous solution in the oxidation step. In the second re-mineralization step, a part of the separated aqueous solution is added to the oxidized and separated solid content to reduce the density of the mineral mud to about 5% solid content.
to about 15% by weight, and subjecting the second remineralizing oxidizing slurry to a second liquid-solid separation step to separate the acid and iron. a second solution containing the acid and a second solid content that is oxidized and separated, and at least a part of the second solution containing the acid and iron is recycled to the first re-mineralization step. It may be circulated. Gold-bearing, iron-bearing sulfide ores that are difficult to smelt can be subjected to a flotation process to produce flotation waste useful as the concentrate and precipitant in the precipitation process. The method may further include cooling the separated aqueous solution prior to use in the oxidation step. The Mg:Fe molar ratio in the slurry in the pressure oxidation process is about 0.5:1 to about
It is advantageous to maintain a sufficient ratio of 10:1 so that the iron precipitated during the pressure oxidation step is more likely to precipitate as hematite rather than other insoluble iron compounds. In the first precipitation step, a precipitant is added to a portion of the solution containing acid and iron to adjust its pH from about 5 to about 8.5.
can be increased to a value in the range of , to precipitate the desired dissolved content while leaving the magnesium ions in solution and recycling at least some of the magnesium-containing solution to the oxidation step to supply magnesium ions thereto. At least a small amount of the slurry from the first re-mineralization process is subjected to a classification process to separate solids larger than a predetermined size from the remaining slurry, and the separated oversized solids are crushed to reduce and feeding the ground solids to at least one of the acidic pretreatment step and the pressure oxidation step, and refluxing the remaining slurry to the step following the first remineralization step. You can also do that. EMBODIMENTS OF THE INVENTION Reference is now made to the accompanying drawings, in which:
By way of example, the drawings show a flow sheet of a method for extracting gold and other metals from gold-containing sulfide concentrates that are difficult to smelt. Referring to the drawings, the difficult-to-smelt gold-bearing sulfide concentrate processed in this embodiment is about 10 to about 800
g/t Au, about 30 to about 300 g/t Ag and about 10 to about 40% Fe by weight, about 5 to about 40% SiO ₂ , about 10 to about 45% S, about 0.1 to about 25% As, about 0.01 to about 3% Sb, about 0.1 to about 6% Al, about 0.1 to about 5% Ca, about 0.1 to about 10% CO ₂ , about 0.1 to about 10% Mg and less than 0.1 to about 8
% of C (organic matter). The sulfide components of such concentrates are:
That is, it may contain one or more of pyrite, arsenopyrite, pyrrhotite, stibnite, and sulfate minerals, and the concentrate may also contain varying amounts of lead, zinc, and copper sulfides. Also, some concentrates may contain oxidizable carbonaceous species. The ore, which has been ground to a content of at least about 70% less than 100 Tyler sieve meshes (less than 149 microns), is fed to a flotation step 12 to produce the aforementioned concentrate along with flotation waste. In the optional re-milling step 14, the concentrate is subjected to the following liquid-solid separation step 16.
Re-grind with water from
325 mesh or less (less than 44 microns). The concentrate slurry from separation step 16 having a mud density of about 40 to about 80 weight percent solids enters an acidic pretreatment step 18 where the slurry is washed of solids from the pressure oxidation step described below. Re-mineralize with acidic cleaning solution. Such acidic cleaning solutions generally contain sulfuric acid and iron, aluminum, magnesium, arsenic and other non-ferrous metals dissolved in the pressure oxidation. Acidic pretreatment is
It decomposes carbonate and acid-consuming gangue components that would otherwise interfere with the pressure oxidation process. The acidic pretreatment step 18 thus also reduces acid consumption in the subsequent pressure oxidation step and lime consumption in the neutralization step described below. In addition, preliminary treatment step 1
It should be noted that No. 8 utilizes in situ generated acid in the subsequent pressure oxidation step. The above treated slurry is further added to concentrate 0.1~10
Prior to oxidation at Kg/t level, it is preferred to add a lignosulfonic acid salt selected from the group consisting of calcium, sodium, potassium and ammonium salts of lignosulfonic acid. The pretreated slurry from pretreatment step 18 enters directly into a pressure oxidation step 20 where the slurry is heated in one or more multichamber autoclaves to about
_{Sulfur ,} Oxidizes arsenic and antimony minerals. Since the presence of free sulfur is detrimental to gold extraction, it is particularly important to oxidize the sulfide to a higher oxidation stage than free sulfur. In such an oxidizing action, iron becomes an effective oxygen transfer agent. It is therefore necessary to have a suitable amount of iron present in solution, especially in the first compartment of the autoclave, which can be achieved by ensuring a sufficiently high and uniform acidity. Moreover, if the acidity and temperature of the autoclave are adjusted so that the desired gold liberation is achieved by oxidation of sulfides, arsenides and antimony compounds to higher oxidation stages, at the same time also the formation of The physical properties of the resulting solids are such that they facilitate subsequent thickening and washing. Acidity and temperature may be adjusted by recycling the acid wash solution and cooling reservoir to the appropriate autoclave compartments, as described in more detail below. Pressure oxidation of pyrite produces ferric sulfate and sulfuric acid. Some of the ferric sulfate will hydrolyze and precipitate as hematite, ferric arsenate, hydronium, dialosite, basic ferric sulfate, or mixtures of these compounds. The nature of the iron species precipitated depends on factors such as temperature, total sulfate content, acidity, mud density, concentrate grade and amount of acid consuming gangue properties. Pressurized oxidation of high grade pyrite and/or arsenopyrite feedstocks with high solids content in the mine mud generally precipitates iron as basic ferric sulfate, hydronium, gyroscope, or ferric arsenate. According to another feature of the invention, the pressure oxidation step 20
Dissolved iron that is hydrolyzed and precipitated by basic ferric sulfate or hydronium may precipitate as hematite rather than as dialosite (reducing lime requirements in the neutralization step prior to cyanidation). It has also been found that such hematite precipitation can be promoted by maintaining a sufficiently high concentration of magnesium in the pressure oxidation step. In the method of the present invention, hematite is a preferred form of iron precipitate, and in that state iron is well liberated in the pressure oxidation step 20 by limestone, which easily removes acid in the first stage precipitation step described below. As a result, it was confirmed that iron precipitates as basic ferric sulfate and/or hydronium dialosite are undesirable for two reasons. Firstly, (a potential lime consumer)
Most of the responsible sulfates pass into the subsequent neutralization step, resulting in high lime consumption. Secondly,
The reaction of lime with basic ferric sulfate and gyrsite converts the iron precipitate into insoluble iron hydroxide and gypsum, resulting in the formation of a muddy precipitate with an increased solids content and a muddy appearance. Increased loss of gold and silver due to adsorption to objects. Thus, it has been determined that there should be sufficient magnesium present in the pressure oxidation step 20 to provide a Mg:Fe molar ratio in the solution of at least about 0.5:1.0, preferably at least about 1:1. Many gold-bearing pyrite ores contain significant amounts of acid-soluble magnesium, at least a portion of the required amount of such magnesium. However, in most cases the gold and sulfide content of the ore is reduced by the flotation process.
2, whereby the oxidation step 20
The magnesium content of the concentrate decreases. At least a portion of the magnesium requirements of the pressure oxidation step 20 may be provided by recirculation of the acidic wash solution and cooling water reservoir described above (to which magnesium ions may be added in the manner described below). can. After a suitable holding time in a pressurized oxidation autoclave, e.g. about 1.5 hours, the oxidized slurry is remineralized with the solution from the subsequent liquid-solid separation step 28 and added in the remineralization step 22. Dilute the slurry to less than 10% solids by weight to obtain the full effect of the agent. The solids from separation step 24 passes to a second mudding step 26 where cooling reservoir water is added to again form a less than 15% by weight slurry. In this way, the re-mineralized slurry is subjected to separation step 2.
8, from where the solution is recycled to the remineralization step 22 as described above. The treatment of the solids from separation step 28 will be described later. The solution from separation step 24 contains acid, dissolved ions, and non-ferrous metal sulfates. Some of this solution is recycled to the acid pretreatment step 18 and pressure oxidation step 20 as described above, and the remaining solution goes to the first precipitation step 30 where lime is added to raise the pH to about 5. It also precipitates metals such as ferric ions, aluminum and arsenic, and removes sulphate sulfur as gypsum. Flotation process 12
The beneficiation waste from can be used in this precipitation step. Then the slurry undergoes the second precipitation step 32
where lime is added to raise the pH to about 10 and precipitate magnesium and other metals. The resulting slurry is subjected to liquid-solid separation step 34.
The relatively pure separated water is passed to a cooling reservoir 36 for subsequent use in the pressure oxidation step 20 and the remineralization step 26 as described above. The solids from separation step 34 can be disposed of as tailings. If desired, the second precipitation step 32 can be replaced by the separation step 3.
4 (as indicated by the dotted box in the drawing), so that the water supplied to the cooling reservoir and subsequently to the pressurized oxidation step 20 and the remineralization step 26 contains magnesium ions. to help maintain the aforementioned desired dissolved magnesium concentration in the pressure oxidation step 20. Also, if desired, a portion of the remineralization slurry from the remineralization step 22 may be passed through a classifier 38 (such as a centrifuge) before being sent to the separation step 24. The classifier 38 removes pre-sorted oversized material, and some of the material is sent to the re-milling step 14.
Some of it is re-milled in the re-milling step 40 and sent to the pressurized oxidation step 20. Such a feature allows the recovery of gold that might otherwise be lost in relatively oversized material that would not be satisfactorily completed in the pressure oxidation step 20. The solids from separation step 28 passes to neutralization step 44 where lime is added to raise the pH to a degree suitable for cyanidation, preferably about 10.5.
Water from the subsequent liquid-solid separation step 47 is added to achieve the desired mud density for cyanidation, ie, about 40 to about 45 weight percent solids. The neutralized slurry then proceeds to a two-stage cyanidation step 46 in which a cyanide solution is added to the first stage. The partially leached mineral mud (60 to 95% leached) is dropped step by step into the eight-stage leachate carbon adsorption section 48 to complete the leaching and collect the dissolved gold and silver. After eight stages, the poor value slurry passes to a liquid-solid separation step 47, the liquid is recycled to the cyanidation step 46 previously described, and the solids are discarded as deposits. The loaded carbon is passed to a metal extraction step 50 where the loaded carbon is stripped under pressure with a caustic cyanide solution and gold and silver are subsequently extracted from the eluate by electrowinning or other suitable means. do. The stripped carbon is regenerated in the kiln, screened and recycled to the leachate carbon adsorption step 48. Examples The feedstock was a gold-bearing concentrate that was difficult to smelt and contained pyrite and arsenopyrite as the primary sulfide minerals. The chemical composition of the concentrate was as follows. Au 236g/t Sb 0.1% As 7.0% CO ₂ 4.2% Fe 24.7% SiO ₂ 21.8% S 19.3% 74% of the gold was extracted by the conventional cyanization method,
A residue containing 60 g/t of Au was obtained. An oxidation feedstock slurry preparation tank, a feed pump system, a four-chamber autoclave with a static capacity of 10L, an autoclave discharge system, an oxidation concentrator supply tank, an oxidation concentrator, and two concentrators and their respective supply tanks. The concentrate was processed in a continuous circuit consisting of a countercurrent decanter wash circuit comprising: The continuous circuit also includes a gold extraction section, where gold is dissolved by cyanidation from the oxidized solids and adsorbed onto the carbon, and a precipitation section, where the acidic effluent is treated with limestone and lime. The arsenic, metals, and associated sulfates were precipitated as arsenates, metal hydroxides, or gypsum, and the metal-depleted solution was recycled to the oxidation and cleaning circuit. The concentrate was pretreated as a 72% solids aqueous slurry in a feed preparation tank with acidic oxidation concentrator overflow solution and diluted to 38% solids. 2.9g/
L As, 14.9g/L Fe (total iron), 2.4g/L Fe
(ferrous iron) and 26.1 g/L of H ₂ SO ₄ at a rate sufficient to give the equivalent of 100 Kg of acid per tonne of concentrate, and the carbonate solution containing 26.1 g/L of H 2 SO 4 was disassembled. Lignosulfonate was also fed to the feed slurry at a level of 1 Kg/t concentrate. The pretreated slurry was pumped into the first chamber of the autoclave. Water was also supplied to the first chamber for temperature control to dilute the solids content of the oxidized slurry to 16.7%. Oxygen was supplied to all rooms. Oxidation was carried out at 185°C and the working pressure was adjusted to 1850 kPa. The nominal retention time of solids in the autoclave was 2.6 hours. Samples were collected from each chamber and the extent of sulfur oxidation and gold liberation was determined by cyanide acceptance testing of the oxidized solids on the samples. The composition, degree of oxidation of sulfur to sulfate, and gold extractability data for representative autoclave solutions obtained under these continuous pressure oxidation conditions are shown in the table below.

Table: The discharge slurry from the autoclave was sent through an evaporation tank to an oxidation concentrator feed tank where it was diluted to approximately 9% solids and fed to the oxidation concentrator. A portion of the oxidation concentrator overflow solution is recycled to the concentrate feedstock pretreatment tank described above, while the remainder is treated with limestone and then with lime in a precipitation circuit to make it metal poor for the cleaning circuit. Got water. The underflow of the oxidizing concentrator, containing 48% solids, was subjected to two-stage cleaning in a countercurrent decanting (CCD) circuit to remove most of the acidic oxidizing liquid. Solid content 53
The underflow of the second washing concentrator, containing %, was processed in a manner conventionally used for gold extraction. Other aspects and embodiments of the invention will be apparent to those skilled in the art, and the scope of the invention is defined in the following claims.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing one example of the steps of the method of the present invention. 12...Flotation process, 14...Re-milling process,
16...Liquid-solid separation process, 18...Acidic pretreatment process, 20...Pressure oxidation process, 22...Re-mineralization process, 24...Liquid-solid separation process, 26...Re-mineralization process Step, 28... Liquid-solid separation step, 30... First stage precipitation step, 32... Second stage precipitation step, 34...
Liquid-solid separation step, 36... Cooling reservoir, 38...
...classifier, 40...re-milling process, 44...neutralization process, 46...two-stage cyanization process, 47...liquid-
Solid separation step, 48...Carbon adsorption part in leachate, 50
...Metal extraction process.

Claims (1)

[Claims] 1. Feeding the concentrate as an aqueous slurry to an acidic pretreatment step; In the acidic pretreatment step, the concentrate is treated with an aqueous sulfuric acid solution to remove carbonates and other acid-consuming gangue compounds. decomposing the above-treated slurry in a pressure oxidation process.
oxidation under a pressurized oxidizing atmosphere at temperatures ranging from 135 to 250°C, during the oxidation process dissolution of iron, formation of sulfuric acid and removal of substantially all oxidizable sulfide compounds from oxidized sulfur. less than 20% of the sulfur is present in the form of elemental sulfur; and water is added to the oxidized slurry in the first re-mineralization step so that the sludge density is between 5 and 5 solids. producing a re-mineralizing oxidized slurry in the range of 15% by weight, subjecting the said re-mineralizing oxidized slurry to a liquid-solid separation process to produce a solution containing acid and iron and an oxidized and separated solid; recirculating a portion of the acid and iron-containing solution to the acidic pretreatment step; and extracting gold from the oxidized and separated solids. A metal containing material that is difficult to smelt, characterized by
A method for extracting gold from iron-bearing concentrates. 2. The method for extracting gold from a gold-containing or iron-containing concentrate that is difficult to smelt, as set forth in claim 1, which comprises recycling a portion of the acid and iron-containing solution to the oxidation step. 3. In the precipitation step, a precipitant is added to a part of the solution containing the acid and iron, so that the metals are converted into their respective hydroxides or hydrated oxides, the sulfate ions are converted into insoluble sulfates, and the arsenic is converted into insoluble arsenic. The difficult-to-smelt metallurgical, iron-bearing method of claim 1, which comprises precipitating as a salt, separating the precipitate from the remaining aqueous solution, and utilizing at least some of the separated aqueous solution in an oxidation step. How to extract gold from concentrate. 4. A method for extracting gold from a gold-containing or iron-containing concentrate that is difficult to smelt, as set forth in claim 3, which comprises cooling the separated aqueous solution before it is used in the oxidation step. 5 Magnesium ions in the slurry in the pressure oxidation step are added to the Mg:Fe molar ratio in the solution of 0.5:
1 to 10:1 so that the iron precipitated during the pressure oxidation step is more likely to precipitate as hematite rather than other insoluble iron compounds. The metal containing material that is difficult to smelt according to item 1;
A method for extracting gold from iron-bearing concentrates. 6. In the first precipitation step, a precipitant is added to a portion of the solution containing acid and iron to raise its pH to a value in the range of 5 to 8.5, thereby precipitating the desired dissolved content and releasing magnesium ions. leaving in solution;
and a method for extracting gold from gold-bearing and iron-bearing concentrates that are difficult to smelt, comprising recycling at least some of the magnesium-containing solution to an oxidation step to supply magnesium ions. 7 In the second re-mineralization step, a part of the separated aqueous solution is added to the oxidized and separated solid content to form a second re-mineral mud with a solid content of 5 to 15% by weight. producing a muddy oxidized slurry; subjecting the second re-mineralized oxidized slurry to a second liquid-solid separation step to produce a second oxidized and separated slurry with a second solution containing acid and iron; and recycling at least a portion of the second solution containing acid and iron to the first re-mineralization step. A method for extracting gold from gold-containing and iron-containing concentrates that are difficult to smelt. 8. Subjecting at least some amount of the slurry from the first re-mineralization step to a classification step to separate solids larger than a predetermined size from the remaining slurry, and grinding the separated oversized solids. supplying the ground solids to at least one of the acidic pretreatment step and the pressure oxidation step; and supplying the remaining slurry to the first re-mineralization step. A method for extracting gold from a gold-containing or iron-containing concentrate that is difficult to smelt, as claimed in claim 1, which comprises refluxing the ore to a subsequent step. 9. Subjecting a gold-bearing and iron-containing sulfide ore that is difficult to smelt to a flotation process to produce the concentrate and flotation waste, and using at least a portion of the flotation waste as a precipitant in the precipitation process. A method for extracting gold from gold-containing or iron-containing concentrate that is difficult to smelt, as set forth in claim 3. 10. The method for extracting gold from gold-containing or iron-containing concentrate that is difficult to smelt, as claimed in claim 1, wherein the treated slurry is oxidized at a temperature in the range of 160 to 200°C. 11. The method for extracting gold from gold-containing or iron-containing concentrate that is difficult to smelt, as set forth in claim 1, wherein the treated slurry is oxidized while maintaining the free acid concentration at 5 to 40 g/L sulfuric acid. 12 The treated slurry is further added to 0.1 to 10
Prior to oxidation at the level of Kg/t concentrate, it is treated by adding a lignosulfonic acid salt selected from the group consisting of calcium, sodium, potassium and ammonium salts of lignosulfonic acid. A method for extracting gold from a gold-containing or iron-containing concentrate that is difficult to smelt as described in item 1.